Re: Variac for ballast

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 7/13/00 8:50:33 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Question: Was my problem due to the magnetizing inrush of current to set
>  the core of the variac? It seemed that I was using an abnormal amount of
>  current but the tank circuit of the coil  wasn't using it. It was almost
>  like the dwell time on the SG was just enough to magnetize the variac
>  core, but not long enough to get past this to be used by the
>  transformer. As soon as I went back to the other reactor, I didn't have
>  the full scale spike in the ammeter every time I energized the circuit,
>  and the coil operated fine at about 1/3 the amperage. If this is true,
>  would wider contacts on the RSG alleviate this problem?
>  
>  Terry
>  

Terry,

I don't think that wider RSG electrodes will help.  How many turns
of the variac were you using?  Was it just a few turns such as 10, or
was the brush near the center of the winding?  It seems that if just a
few turns are used, the core will saturate, because saturation depends
on voltage vs. number of turns.  When I tried the variac type ballast on 
my coil, i was using only a few turns, and the system drew double the
normal power for the same spark length because of the saturation.  
I normally use a homemade ballast which is simply a few layers of
#12 wire wound on a pvc form, with transformer iron inside.

Some folks cut a slot into the variac core to prevent saturation, but 
this ruins the variac for other purposes.  It might help if you add some
resistive ballast to clip off some of the power peaks, but when I tried
adding resistive ballast in my system with the variac-type ballast, it
didn't help any.

Cheers,
John Freau